Provided by: tpm2-tools_5.4-1_amd64 bug

NAME

       tpm2_startauthsession(1) - Start a session with the TPM.

SYNOPSIS

       tpm2_startauthsession [OPTIONS]

DESCRIPTION

       tpm2_startauthsession(1) - Starts a session with the TPM.  The default is to start a trial
       session unless the -a option is specified.  Saves the policy session data to a file.  This
       file  can then be used in subsequent tools that can use a policy file for authorization or
       policy events.

       This   will   not   work   with   resource   managers   (RMs)   outside   of    tpm2-abrmd
       (https://github.com/tpm2-software/tpm2-abrmd), as most RMs will flush session handles when
       a client disconnects from the IPC channel.  However, when using a RM without  the  session
       gapping feature, one can use the command TCTI to keep the connection open.

       The first step is to create a socket listener that uses tpm2_send:

              mknod "$HOME/backpipe" p
              while [ 1 ]; do tpm2_send 0<"$HOME/backpipe" | nc -lU "$HOME/sock" 1>"$HOME/backpipe"; done;

       The next step is to use the command TCTI and netcat (nc) to send data to the socket.

              tpm2_startauthsession --tcti="cmd:nc -q 0 -U $HOME/sock" <options>

       When  finishing  ensure to kill the listener.  For commands executed with the command tcti
       against the listener, one will need to manage transient handles.  The simplest way  is  to
       add a flush after each command: tpm2_flushcontext --tcti="cmd:nc -q 0 -U $HOME/sock" -t

       Note:  This  example  uses  UNIX sockets, since the socket is controlled with Linux access
       controls.  Using a port is not recommended as it’s either open to any user on  the  system
       (localhost) or bound to a network card and exposed to the network.

       This  will  work with direct TPM access, but note that internally this calls a ContextSave
       and a ContextLoad on the session handle, thus the session cannot be saved/loaded again.

OPTIONS

--policy-session:

         Start  a  policy  session  of  type  TPM_SE_POLICY.   Default  without  this  option  is
         TPM_SE_TRIAL.

         NOTE:  A  trial session is used when building a policy and a policy session is used when
         authenticating with a policy.

       • --audit-session:

         Start an HMAC session to be used as an audit session.  Default without  this  option  is
         TPM2_SE_TRIAL.

       • --hmac-session:

         Start   an   HMAC   session  of  type  TPM_SE_HMAC.   Default  without  this  option  is
         TPM2_SE_TRIAL.

       • -g, --hash-algorithm=ALGORITHM:

         The hash algorithm used in computation of the policy digest.

       • -G, --key-algorithm=ALGORITHM:

         The symmetric algorithm used in parameter encryption/decryption.

       • -c, --key-context=OBJECT:

         Set the tpmkey and bind objects to be the same.  Session parameter encryption is  turned
         on.   Session  parameter  decryption  is  turned  on.   Parameter  encryption/decryption
         symmetric-key set to AES-CFB.

       • -S, --session=FILE:

         The name of the policy session file, required.

       • --bind-context=FILE:

         Set the bind object.  Session parameter encryption is off.   Use  tpm2_sessionconfig  to
         turn  on.   Session  parameter  decryption  is  off.  Use tpm2_sessionconfig to turn on.
         Parameter encryption/decryption symmetric-key set to AES-CFB.

       • --bind-auth=AUTH:

         Set the authorization value for the bind object.

       • --tpmkey-context=FILE:

         Set the tpmkey object.  Session parameter encryption is off.  Use tpm2_sessionconfig  to
         turn  on.   Session  parameter  decryption  is  off.  Use tpm2_sessionconfig to turn on.
         Parameter encryption/decryption symmetric-key set to AES-CFB.

       • -n, --name=FILE

         A name file as output from a tool like tpm2_readpublic(1) -n option.  The name file  can
         be  used  to  verify  a persistent handle input for the --tpmkey-context, -c, and --key-
         context options.  Verification that the object referenced by  a  peristent  handle,  e.g
         0x81000000,  is  the key expected prevents attackers from performing a man-in-the-middle
         attack on session traffic.

   References

Context Object Format

       The type of a context object, whether it is a handle or file name, is determined according
       to the following logic in-order:

       • If  the  argument  is  a  file path, then the file is loaded as a restored TPM transient
         object.

       • If the argument is a prefix match on one of:

         • owner: the owner hierarchy

         • platform: the platform hierarchy

         • endorsement: the endorsement hierarchy

         • lockout: the lockout control persistent object

       • If the argument argument can be loaded as a  number  it  will  be  treat  as  a  handle,
         e.g. 0x81010013 and used directly._OBJECT_.

Authorization Formatting

       Authorization  for  use of an object in TPM2.0 can come in 3 different forms: 1.  Password
       2.  HMAC 3.  Sessions

       NOTE: “Authorizations default to the EMPTY PASSWORD when not specified”.

   Passwords
       Passwords are interpreted in the following forms below using prefix identifiers.

       Note: By default passwords are assumed to be in the string form when they do  not  have  a
       prefix.

   String
       A  string password, specified by prefix “str:” or it’s absence (raw string without prefix)
       is not interpreted, and is directly used for authorization.

   Examples
              foobar
              str:foobar

   Hex-string
       A hex-string password, specified by prefix “hex:” is converted  from  a  hexidecimal  form
       into  a  byte  array  form, thus allowing passwords with non-printable and/or terminal un-
       friendly characters.

   Example
              hex:1122334455667788

   File
       A file based password, specified be prefix “file:” should be the path of a file containing
       the  password  to  be  read by the tool or a “-” to use stdin.  Storing passwords in files
       prevents information leakage, passwords passed as options can be  read  from  the  process
       list or common shell history features.

   Examples
              # to use stdin and be prompted
              file:-

              # to use a file from a path
              file:path/to/password/file

              # to echo a password via stdin:
              echo foobar | tpm2_tool -p file:-

              # to use a bash here-string via stdin:

              tpm2_tool -p file:- <<< foobar

   Sessions
       When  using a policy session to authorize the use of an object, prefix the option argument
       with the session keyword.  Then indicate a path to a session file that  was  created  with
       tpm2_startauthsession(1).   Optionally,  if  the session requires an auth value to be sent
       with the session handle (eg policy password), then append a + and a string as described in
       the Passwords section.

   Examples
       To use a session context file called session.ctx.

              session:session.ctx

       To use a session context file called session.ctx AND send the authvalue mypassword.

              session:session.ctx+mypassword

       To use a session context file called session.ctx AND send the HEX authvalue 0x11223344.

              session:session.ctx+hex:11223344

   PCR Authorizations
       You  can  satisfy  a PCR policy using the “pcr:” prefix and the PCR minilanguage.  The PCR
       minilanguage is as follows: <pcr-spec>=<raw-pcr-file>

       The PCR spec is documented in in the section “PCR bank specifiers”.

       The raw-pcr-file is an optional argument that contains the output of the raw PCR  contents
       as returned by tpm2_pcrread(1).

       PCR bank specifiers

   Examples
       To satisfy a PCR policy of sha256 on banks 0, 1, 2 and 3 use a specifier of:

              pcr:sha256:0,1,2,3

       specifying AUTH.

COMMON OPTIONS

       This  collection  of options are common to many programs and provide information that many
       users may expect.

       • -h, --help=[man|no-man]: Display the tools manpage.  By default, it attempts  to  invoke
         the  manpager  for the tool, however, on failure will output a short tool summary.  This
         is the same behavior if the “man” option argument  is  specified,  however  if  explicit
         “man”  is  requested,  the tool will provide errors from man on stderr.  If the “no-man”
         option if specified, or the manpager fails, the short options will be output to stdout.

         To successfully use the manpages feature requires the manpages to  be  installed  or  on
         MANPATH, See man(1) for more details.

       • -v, --version: Display version information for this tool, supported tctis and exit.

       • -V,  --verbose:  Increase the information that the tool prints to the console during its
         execution.  When using this option the file and line number are printed.

       • -Q, --quiet: Silence normal tool output to stdout.

       • -Z, --enable-errata: Enable the application of errata fixups.  Useful if an errata fixup
         needs   to   be  applied  to  commands  sent  to  the  TPM.   Defining  the  environment
         TPM2TOOLS_ENABLE_ERRATA is equivalent.  information many users may expect.

TCTI Configuration

       The TCTI or “Transmission Interface” is the communication mechanism with the  TPM.   TCTIs
       can be changed for communication with TPMs across different mediums.

       To control the TCTI, the tools respect:

       1. The command line option -T or --tcti

       2. The environment variable: TPM2TOOLS_TCTI.

       Note: The command line option always overrides the environment variable.

       The current known TCTIs are:

       • tabrmd         -         The        resource        manager,        called        tabrmd
         (https://github.com/tpm2-software/tpm2-abrmd).  Note that tabrmd and  abrmd  as  a  tcti
         name are synonymous.

       • mssim - Typically used for communicating to the TPM software simulator.

       • device - Used when talking directly to a TPM device file.

       • none - Do not initalize a connection with the TPM.  Some tools allow for off-tpm options
         and thus support not using a TCTI.  Tools  that  do  not  support  it  will  error  when
         attempted  to  be used without a TCTI connection.  Does not support ANY options and MUST
         BE presented as the exact text of “none”.

       The arguments to either the command line option or the environment  variable  are  in  the
       form:

       <tcti-name>:<tcti-option-config>

       Specifying  an  empty string for either the <tcti-name> or <tcti-option-config> results in
       the default being used for that portion respectively.

   TCTI Defaults
       When a TCTI is not specified, the default TCTI is searched for using dlopen(3)  semantics.
       The  tools  will search for tabrmd, device and mssim TCTIs IN THAT ORDER and USE THE FIRST
       ONE FOUND.  You can query what TCTI will be chosen as the default by using the  -v  option
       to  print  the version information.  The “default-tcti” key-value pair will indicate which
       of the aforementioned TCTIs is the default.

   Custom TCTIs
       Any TCTI that implements the dynamic TCTI interface can be loaded.  The  tools  internally
       use  dlopen(3), and the raw tcti-name value is used for the lookup.  Thus, this could be a
       path to the shared library, or a library name as understood by dlopen(3) semantics.

TCTI OPTIONS

       This collection of options are used to configure the various known TCTI modules available:

       • device: For the device TCTI, the TPM character device file for use by  the  device  TCTI
         can be specified.  The default is /dev/tpm0.

         Example: -T device:/dev/tpm0 or export TPM2TOOLS_TCTI=“device:/dev/tpm0”mssim:  For  the  mssim  TCTI, the domain name or IP address and port number used by the
         simulator can be specified.  The default are 127.0.0.1 and 2321.

         Example:          -T          mssim:host=localhost,port=2321          or          export
         TPM2TOOLS_TCTI=“mssim:host=localhost,port=2321”abrmd:  For  the  abrmd  TCTI, the configuration string format is a series of simple key
         value pairs separated by a `,' character.  Each key and value string are separated by  a
         `=' character.

         • TCTI abrmd supports two keys:

           1. `bus_name' : The name of the tabrmd service on the bus (a string).

           2. `bus_type'  :  The  type  of  the dbus instance (a string) limited to `session' and
              `system'.

         Specify the tabrmd tcti name and a config string of bus_name=com.example.FooBar:

                \--tcti=tabrmd:bus_name=com.example.FooBar

         Specify the default (abrmd) tcti and a config string of bus_type=session:

                \--tcti:bus_type=session

         NOTE: abrmd and tabrmd are synonymous.  the various known TCTI modules.  # EXAMPLES

   Start a trial session and save the session data to a file
              tpm2_startauthsession -S mysession.ctx

   Start a policy session and save the session data to a file
              tpm2_startauthsession --policy-session -S mysession.ctx

   Start an encrypted and bound policy session and save the session data to a file
              tpm2_createprimary -c primary.ctx
              tpm2_startauthsession --policy-session -c primary.ctx -S mysession.ctx

Returns

       Tools can return any of the following codes:

       • 0 - Success.

       • 1 - General non-specific error.

       • 2 - Options handling error.

       • 3 - Authentication error.

       • 4 - TCTI related error.

       • 5 - Non supported scheme.  Applicable to tpm2_testparams.

BUGS

       Github Issues (https://github.com/tpm2-software/tpm2-tools/issues)

HELP

       See the Mailing List (https://lists.linuxfoundation.org/mailman/listinfo/tpm2)